The present invention relates to a data processing apparatus having a built-in electrically rewritable nonvolatile flash memory. Further, the present invention relates to a technology which makes the built-in flash memory rewritable by use of an external device such as a PROM writer in the same way as a discrete flash memory, and to a technology which is useful when applied to a microcomputer, for example.
JP-A-161469 (laid-open on Jun. 26, 1989 and corresponding to U.S. Application No. 116,607 filed on Nov. 3, 1987) describes a microcomputer having an EPROM (Erasable and Programmable Read-Only Memories) or an EEPROM (Electrically Erasable and Programmable Read-Only Memories) as a programmable nonvolatile memory formed in a single semiconductor chip. Programs and data are held in such a nonvolatile memory disposed in the on-chip arrangement in the microcomputer. Since the EPROM needs ultraviolet rays to erase the stored data, rewrite cannot be effected unless the chip is removed from the applied system. Meanwhile, since the EEPROM can be electrically erased and written, the stored data can be rewritten with the EEPROM mounted onto the system. However, since memory cells constituting the EEPROM need select transistors besides the memory elements, such as MNOSs (Metal Nitride Oxide Semiconductors), the size of the memory cell becomes about 2.5 to 5 times as large as that of the memory cell of the EPROM. Therefore, a relatively large area of the chip is necessary for the nonvolatile flash memory portion.
JP-A-2-289997 (laid-open on Nov. 29, 1990) describes a simultaneous erase type EEPROM. This simultaneous erase type EEPROM is synonymous to the flash memory disclosed in this specification. Data of the flash memory can be rewritten by implementing a sequence of electrical erase and write operations, and the memory cell of this flash memory can be constituted by one transistor in the same way as the EPROM. Further, the flash memory has the function of simultaneously, electrically erasing all the memory cells as a bulk or, alternatively, one or more blocks of memory cells. Therefore, the stored data of the flash memory can be rewritten with the flash memory kept mounted on the system (in the on-board state). This simultaneous erase function can shorten the rewrite time, and also contributes to the reduction of the chip occupying area.
U.S. Pat. No. 4,701,886 issued on Oct. 20, 1987 to Y. Sakakibara et al discloses a one-chip microcomputer having an EPROM. Data stored in that EPROM can be changed by externally supplying new data thereto from an EPROM writer.
U.S. Pat. No. 4,807,114 issued on Feb. 21, 1989 to S. Itoh discloses a microcomputer which is programmable either externally or by its internal control function.